1. Field of the Invention
The present invention relates to a stage for holding a wafer during semiconductor device fabrication and, more particularly, to a stage which is heated in order to prevent particles in the air from accumulating on the wafer.
2. Discussion of Related Art
In general, semiconductor device fabrication involves multiple steps, including: a diffusion step for forming a thin film on the surface of a wafer; a heat treatment step; a photographic process for forming a previously set pattern on the wafer surface; an etching process for realizing the pattern; an ion implanting process for producing an intended electric characteristic in the film; and a thin film process for making the film thinner and more uniform. After these processes, the wafer is examined in a testing/measuring process to determine whether the desired effect has been achieved.
Testing/measuring facilities are designed specifically to test each wafer one at a time after each wafer is laid on a stage. The wafer is transported and tested while on this stage.
An example of a stage used in the testing/measuring processes is illustrated in the loadlock chamber of FIG. 1. The loadlock chamber serves as an airlock for a test chamber. The loadlock chamber has a wafer holder arm 4 and a stage 5 which is placed under the holder arm 4 in the load chamber 1. The loadlock chamber 1 further has an inner gate 2 and an outer gate 3. In the case where the loadlock chamber is used with a vacuum test chamber, the outer gate 3 is opened while the inner gate 2 is closed in order to protect the vacuum test chamber from the outside air. In that state, a wafer (not shown) is inserted and laid on the stage 5. Then, the outer gate 3 is closed and air from inside the loadlock chamber is removed by a suctioning process until its pressure matches the predetermined low pressure of the vacuum test chamber. Then the inner gate 2 is opened so that the wafer on the stage 5 of the load chamber can be moved to the vacuum test chamber.
However, even though the loadlock chamber is used in a clean room, each wafer is exposed to the air before being inserted into the test chamber. Therefore, particles remaining in the fresh air in the clean room or falling from the facilities or introduced by a worker, may accumulate or adhere onto the wafer. This contaminates the wafer 6, causes the product to be defective, and thus decreases the yield of the semiconductor device fabricating process.